squaring up large areas

[yakka]

I usually use diagonals or 3m - 4m - 5m formula to square up.. My question is what methods do you use over large areas e.g.: 40 x 30m to ensure you get a nice perfectly set rectangle :o
<O:p</O:p


Cheers yakka

[David L]

Good question I was wondering that my self.
I am stuck with the 3,4,5, formula too.

[ozwinner]

Measure the diagonals.

If you have an odd shape, run string lines to create a rectangle and measure the diagonals of the rectangle, then take and measuements for the odd shape from that.

Al :cool:

[bitingmidge]

I use a surveyor.

If you need accuracy over that sort of area, and can't handle a theodolite, that's your only solution.

If it's farm work or whatever, you could use a GPS.

Cheers,

P

[Vernonv]

Sorry to disagree bitingmidge, but I wouldn't use a GPS unless you can afford to be up to 20m out (or more).

[Vernonv]

Thinking out aloud ...

1. Mark out one corner using the 3,4,5 rule (or 6,8,10 or 9,12,15 or ...) and then use a string line from the corner and through a vertices's (sp?) to the other corner. Once you have two sides, then next two shouldn't be difficult.

2. Measure out 30m, 40m and 50m of string/rope.

[Chesand]

5, 12, 13 also works. 5 & 12 are the sides, 13 the hypotenuse if it is sqaure

[bitingmidge]

Sorry to disagree bitingmidge, but I wouldn't use a GPS unless you can afford to be up to 20m out (or more).

Ahh yes, sorry. You'd have to know a surveyor with a fair dinkum one! :rolleyes:

Cheers,

P

[Vernonv]

You'd have to know a surveyor with a fair dinkum one!

Yep, one of those would work a treat. Very accurate bit of gear, but also very expensive.

[chrisp]

Yes, Differential GPS. Funny stuff. The US sets up the GPS system and realises that maybe an adversary may also able to use it for military purposes. Solution - introduce a secret "random" error into the system. The US navy then sets up correction signals that transmit the error corrections so you can remove the errors (later) - this is differential GPS. From memory differential GPS is accurate to about 10-20cm.

[outback]

Sorry to disagree bitingmidge, but I wouldn't use a GPS unless you can afford to be up to 20m out (or more).


Of course farmers which use gps with an accuracy of 2 cm wouldn't count I guess. :rolleyes:

[bitingmidge]

Of course farmers which use gps with an accuracy of 2 cm wouldn't count I guess. :rolleyes:

Same system as the surveyors, not your $100 Tandy variety!

Mind you, I've used "farmer's levels" a bit and they have a "surprising" level of accuracy! :D :D :D

Cheers,

P

[Vernonv]

Other than for cropping (mainly), there aren't too many farmers around that have/use high accuracy positioning systems.

I'm always amazed at the number of people (not just farmers) that expect their $200 GPS received to be accurate to the metre (or sub-metre).

Even the 5 metre accuracy most receivers quote in nearly impossible to achieve under normal usage conditions.

[joe greiner]

Over that large an area, a string or rope will stretch too much to provide reliable measurements. Best bet is to hire a surveyor. Alternatively, use a steel tape to measure each leg and hypotenuse. If your tape is too short, lay out a smaller rectangle at one corner, and extend its legs in the required directions. In either case, use a spring scale at the pulling end of the tape to assure the same tension in the tape for each measurement. For the shorter tape, re-check the overall diagonals by using taut string for alignment, and measure segments with the tape and spring scale.

Joe
retired civil engineer, but not a surveyor

[TEEJAY]

Over that large an area, a string or rope will stretch too much to provide reliable measurements. Best bet is to hire a surveyor. Alternatively, use a steel tape to measure each leg and hypotenuse. If your tape is too short, lay out a smaller rectangle at one corner, and extend its legs in the required directions. In either case, use a spring scale at the pulling end of the tape to assure the same tension in the tape for each measurement. For the shorter tape, re-check the overall diagonals by using taut string for alignment, and measure segments with the tape and spring scale.

Joe
retired civil engineer, but not a surveyor

Yep and don't forget to take into account the thermal effects upon the tape as it is calibrated to give accurate results at given tension and given temperature.

It depends upon what degree of accuracy you are after - most formwork is + - 10mm so reasonable tolerances are probably all you are after and a tape with consistent tension is most likely adequate.

I'm with Joe

[ian]

I usually use diagonals or 3m - 4m - 5m formula to square up.. My question is what methods do you use over large areas e.g.: 40 x 30m to ensure you get a nice perfectly set rectangle :o
<O:p</O:p


Cheers yakkadefine "perfectly set rectangle"
how much "out of square" error can you tollerate?

and before you answer, can you tell if the area you want to plant the rectangle is on level?

if you have a spring balance and a 50m steel or cloth tape, you can set out the rectangle because just like the 3:4:5 triangle
30 squared + 40 squared = 50 squared (900 + 1600 = 2500 = 50x50)
important points

both ends of the tape must be at the same level which is not the same as the same distance off the ground
the tape must not touch the ground anywhere
all measurements must be made with the same reading on the spring balance
lay out the 40m long side
then from one end lay out the 30m side, drawing an arc on the ground roughly where the corner should be
lay out the 50m diaganal – where the diaganal intersects the arc, is where the corner is
repeat for the 4th cornerif you need to be accurate to a few cms you'll need to correct for temperature and hiring a surveyor is probably the easiest option.
Especially so if the site isn't level or if the layout is for a prefab shed.


ian

[joe greiner]

I was going to just postscript a suggestion to measure at night to reduce temperature effects. But a further question arises: To paraphrase ian, how "perfect" does it have to be? Most structures should have some local adjustment built into the design. Large equipment such as newspaper printing presses, long-line machining centers and such come to mind. In such a case, a surveyor would be mandatory.

In an earlier career in the precast architectural concrete game, we always allowed a minimum of 25mm clearance to anything we didn't control, such as the building frame, and made up the gaps in the connection design. Then for the odd-ball cases, we made the specials to fit after the main parts had been erected.

Joe

[journeyman Mick]

Like TeeJay says, it depends what degree of accuracy you're after. I've only ever used profiles, stringlines and tapes. Unless your building something like a hospital or a shopping centre you don't need to get any more accurate than this will allow.

Mick

[cyberhonky]

guys- further to what Ian said- the hypotenuse (A) is the square root of sum of X and Y squared (see sheet attached) just change the numbers for your dimensions.

[Barry_White]

Like Mick and Al says if it is for a prefab shed using the profiles is all that is necessary and set out the first corner with the 3, 4, 5 method and then just measure the diagonals using a steel tape.

This was how we set out sheds and there is enough tolerance in them to allow for minor discrepancies and 30 x 40 metres is not that big really and if it was a shed being built on a slab the ground would have been leveled first.

Our guys used to set out piers for sheds with the ground up to 1200mm out of level over 40 metres.

[Ivan in Oz]

5, 12, 13 also works. 5 & 12 are the sides, 13 the hypotenuse if it is sqaure

Chesand,
You took the easy one:mad:
OK
9, 40, and Hyp is 41

Wanna be a mighty long piece of Timber:D

[Barry_White]

For those that have Microsoft Excel here is a Hypotenuse Calculator.

[Ekim]

If you want to use the square root method (see Cyberhonky’s post above), then using the cell references in Bazza’a Excel model, the Excel formula for the Hypotenuse is:

=SQRT((POWER(F15,2)+POWER(I11,2)))

[John99]

why not do it of a night and use the stars !:eek:

[outback]

Other than for cropping (mainly), there aren't too many farmers around that have/use high accuracy positioning systems.

I'm always amazed at the number of people (not just farmers) that expect their $200 GPS received to be accurate to the metre (or sub-metre).

Even the 5 metre accuracy most receivers quote in nearly impossible to achieve under normal usage conditions.
Ya gotta understand these farmers are after -2.5cm accuracy. Probably less than most shopping centres. Yes, for cropping only, but thats prestty impressive for 1000 acres. :eek:

[ian]

why not do it of a night and use the stars !:eek:I take it you have an atomic clock and a transit telescope :D

[Ivan in Oz]

why not do it of a night and use the stars !:eek:


Why not do it at night and you will have difficulty in seeing any errors:eek:
No Stars and
you will have difficulty in seeing anything much at ALL:D ;) :o